Process of making a battery separator



E. c. UHLIG ETAL 2,662,032

PROCESS 0F' MAKING A BATTERY SEPARATOR Filed Aug. 4, 1951 c 2 Sheets-Sheet l Dec. 8, 1953 ATTORNEY PROCESS oF MAKING A BATTERY 'sEPARAToR Filed Aug. 4, 1951 2 sneetssneet 2 DRY ATTORNEY Patented Dec. 8, 1953 UNITED STATES PROCESS 0F MAKING A BATTERY` SEPARATOR Edwin C. Uhlig, Greenwood, and Linwood A. Murray, Jr., Cranston, R. I., assignors tc United States Rubber Company, New York, N. Y., a corporation of New Jersey Application August 4, 1951, Serial No. 240,315 K 5 Claims.

This invention relates te iiquid permeame battery separators and more particularly to separators of the type which are made by impregnation of a bibulous cellulosic fibrous sheet material having a high alpha cellulose content with a solution of an A-stage phenol-formaldehyde resin in water or other aqueous medium, drying the sheet to remove the water and other volatile material and subsequently heating the impregnated sheet to convert the resin to the C-stage. Battery separators of this general type are shown in U. S. patent to Uber 2,543,137 and inour copending applications Serial Nos. 240,312 and 240,314 led of even date herewith.

The principal object of the presentrinvention Y- is to provide a battery separator of the above type which contains uniformly distributed therethrough a wetting agent which facilitates wetting and penetration of the separator by the battery acid when the battery is to be prepared for service. Another object is to provide such a separator in which the wetting agent is so applied and distributed that new results are achieved. Another object is to provide a process of making a battery separator of the above type wherein the wetting agent is divided into two portions which are applied in different ways and at different points in the process whereby a new cooperation between the two portions of the wetting agent is achieved.

Another object is to apply the wetting agent in A such a way that new results are obtained as compared to those which would be obtained were the entire portion of the wetting agent applied either in solution in the aqueous solution of the A-stage phenolic resin used for impregnating the cellulosic sheet or to the cured sheet or separator cut therefrom. Numerous other objects of our invention will be apparent to those skilled in the art.

In the accompanying drawings: y

Fig. 1 is a plan view of a separator made in accordance with our invention;

Fig. 2 is a sectional view of the separator of Fig. 1 taken on the line 2-2 thereof;

Fig. 3 is a flow diagram of the production of battery separators in accordance with the present invention.

The present invention is based upon our discovery that new and advantageous results are achieved if the wetting agent `is introduced in two separate portions which are applied in different ways. We have found that better and far more eiective utilization of the wetting agent is achieved if a portion only thereof is dissolved in the aqueous solution of theA-stage phenolsul ' formaldehyde resin used for impregnating the bibulous cellulosic fibrous sheet and if the balance of the wetting agent is applied, preferably in the form of an aqueous solution thereof, to the cured sheet or separator, i. e., in which'the resin has been heated to convert it from the A-stage to the C-stage. We much prefer to apply an aqueous solution of the second portion of the wetting agent to the cured sheet immediately or shortly after it emerges from the curing zone and while the sheet is at a temperature of from 300 to 500 F. This temperature represents residual heat left in the sheet by the curing step` which is usually carried out at temperatures ranging from 300 to 550 F. and preferably at from 400 to 500 F. c

Y We have round that applicationv of the wetting agent in the manner ldescribed above effects new results in that that portion of the wetting agent which is Vdistributed throughout the cured impregnated sheet as a result of solution thereof in the aqueous resin solution used for impregnating the original base sheet greatly facilitates subsequent penetration of the cured sheet by the aqueous solution of the balance of the wetting agent. We nd that the results thus achieved are far superior to those which would be obtained if one attempted to apply the same total amount of wetting agent either in solution in the aqueous solution of the A-stage resin or as an aqueous solution applied to the cured sheet. Thus, if one attempted to introduce the saine total amount of wetting agent in solution in the impregnating resin solution the properties of the cured resin would be injured and the properties of the resulting separator would be impaired assuming that the amount of wetting agent so appliedwere sufficient to bring about the desired rapid penetration of the battery acid into the separator. Consequently it is impossible to secure our results merely by increasing the amount of wetting agent dissolved in the resin solution. On Vtheother hand, if the wetting agent is omitted from the resin solution and it is attempted to introduce the entire amountcf the wetting agent by ap-V plication of an aqueous solution thereof to the cured sheet, the results are unsatisfactory because the wetting agent cannot properly penetrate the sheet so as to cause good penetration of the battery acid. However, by adding part of the wetting agent to the aqueous resin solution used to impregnate the fibrous sheet and applying the rest of the wetting agent in the form of an aqueous solution in any suitable manner, as by immersion, spraying or other coating method to the cured sheet, the initially introduced portion of wetting agent left upon drying and curing is so uniformly distributed throughout the cured sheet that when the rest of the wetting agent is applied thereto it rapidly and uniformly penetrates the sheet. Thus, there is a new coaction between the two separately applied portions of wetting agent and not only is commercial production of the battery separator greatly facilitated but the resultingfseparator is I far superior in use.

The presence in the cured sheet of a small amount of wetting agent, insucient by itself to effect the desired wetting of thejfinished separator by the battery acid, as a result of incorporation with the aqueous A-stage resin solution, is eiective to promote complete penetration `of' the cured sheet by the subsequently applied aqueous solution of the balance of the wetting agent. Evidently the first portion of the wetting agent is,upon drying, ydistributed throughout 'the resin .phasein an' unusually uniform'andfhighly extended form, :so that 'there are 'present Iinterlaced continuousiphases of resinan-d of wetting agent, vthe latter `of course beingin very minor proportion but nevertheless --being exposed over the entire surface-of the lresin phase so that the later-applied wetting agent is completely and uniformly ydistributed throughout the cured resin phase.

In ypracticing our invention, we prefer lto employ the procedure described in detail in our above-identified copending applications which are specifically directed to employing water in a'dmixture with a speciiiedlproportion of a lower (C1 to C3) alkanol or acetone to dissolve the A-stage phenol-'formaldehyde resin. VHowever, the instant-invention-isvnot-limited'to use with that procedure A,but can-beapplied with advantageous results -to lbattery separator Yproduction wherein the 'solvent for -the A-stage resin con- 'sists of water as taught by 'the l above-mentioned Ujoe-r jpa-tent.

In practicing 'our' invention we take a bibulous cellulosicbrous'sheet containing at least 90% -of alpha cellulose, -havi-ng an a-ir permeability '(Gurley) of-'from 1 to l'secondsand athickness of from 02028 1100.038 and also exhibiting uniformforma-tion, and-impregnate `it -with an aqueous lsolution of `the phenol-formaldehyde resin' anda portion of the *wetting agent in such awaytha-t -from :Z5-to 50%of'resin,basedfon ber plus resin, is introduced l'into the sheet in such away that upon curing the @fibers are protected against battery acid but the air Apermeability -of the sheet fis not v'materially lowered. We "then dry the sheet, embossthe dried'sheet `to form ribs in theform Aof integral protuberantportions on oneside thereof and-correspondingdepressed portions on-the Vother side, and cure the Vembossed `sheet typically at 30G-1550MB, and preferably at 400=500 F., to advance the resin `to the iC-stage. Wethen apply, 'typically by spraying, la-naq-ueous solution of the balance of the wetting agent `to the hot cured sheet 'as it leaves the `curing zone and vso is at `an elevated Itemperature, typically at300-'500*F., byrreason of residualh'eat from the curing step. We then cut the sheet to width and'length to form .the nished battery separator. At .some time in the operation, after application ofthe second portionof wetting agent, we allow the sheet ,or the .separators cut therefrom to stand for severalhours, e. g., forat least 5'hours, vpreferably `under relatively non-.evaporative Vconr'ditions, to allow the aqueous solution ofthe secsheet.

4 ond portion of the wetting agent to uniformly and throughly impregnate the entire structure of the sheet. Some of the water of the wetting agent solution unavoidably evaporates because of the relatively high temperature of the cured sheet, vbut under ordinary-:conditions sufficient water of solutionremains'to insure this-1 uniform distribution of the second portion of wetting `agent if the separators are allowed to stand for say 5 to 10 .hours under conditions such that further evaporation of water is prevented or considerably retarded. Such relatively nonevaporati-ve'conditions can be attained in any suitable Amanner, as by placing a stack of the separatorsina suitable enclosure, e. g., the container in which'they are to be shipped, and al- .lowing :themto1stand therein for the requisite periodof time. The water content of the solution of the wetting agent in the sheet or separators during this standing period should be sufciently greatto hold thatiportiontofi'the wetting agent which wasadded. after .curing. in: solution. 'If vprecipitation .of fthe wetting agent zinsolid formoccurs 'before complete penetration,-a non'- uniform productA may result. The.` separators are nowl readyforuse; inthe battery. Becauseoof :the peculiar distribution of the -wetting agent achieved bythe.v present inventionxthefseparators are unusually;Y satisfactory. they fare v4very rapide lyV andthoroughly penetrated-bythe battery fac-'1d when placed .in service.

The 'total amount of 1wetting;agent iintroducerl into the :separator by our `invention' can vary widely. The amount canrangeasilowas .1% to as high Yas v210% based-.fon the resin '.content of the separator. "We .prefer to use ian ,amount equal to from f 2 vto ,4% ibased onreSin. .Theadistribution of fthe wetting agent :'loetweenl that '.applied with thefresin solution and that-subsequentlyappl-ied-.to the cured -sheetfzcandikewise vary Widely. 'Typically .weintroducerfrom`1/21to 4% yby weight of -wetting agent basedon -resinpwith the loriginal resin v solution and later apply from 1A.; to-6% l'byweightfof wetting ;agent,fbased.on resin, to v-thehot cured sheet. Vl/Vefprefer yto-.apply from 1/2 toll/2% ('basedfhnresin) `:of .wetting agent in the :aqueous A-stage yresin-.solutionand to later apply from `1 Ito 2% :by Weight (based on resin) .ofv wetting agent :to .the hotrcured -We .secure v-very `advantageous ,results :by 'applying 1% .of wettingzagent .in theresiny solution and-1i1/2% of wetting agent tothe hotcured sheet, these percentages vof wetting agent 'again being' by Weight-'basedf-up'on :the resin contenter the sheet.

`We typically introduce from oneethird lto sone,- half of Vthe entire Vamount-of -wetting :agent .1in solution intheimpregnating resin -solution:and the balance, correspondingly ranging from .twothirds to one-half;tofthe.=curedl sheet.

We canusefany wettingagent 1which is'effective to promote wetting A4ofthe-celelulos-ic Sflbersbby the aqueous resin solution andsubsequentwetting of the resin-coated fibers-of the-separator`by .the Vbattery 4acid :and which Ldoes not introduce :an objectionable contaminating iniiuer-iee when Athe battery acid is added. Any of the We'll =known wetting agents stable ito battery '-acid vcan' bezemployed. Wev especially prefer to use :the alkali metal salts Jof sulfated fatty alcoholshaving fat least 8 carbon a-tornsper molecule, e.ig.,sodium dodecyl sulfate, sodium oleyl sulfate, etc. Examples of -such 'alkali meta-l salts of sulfated fatty alcohols arethe-wetting agentssold' commercially Vunder Tthe trade name v"Iergitol. Another example 'of 'a' suitable waningv agent 'is that sold `as Aerosol OT whichisadioctyl ester of sodium sulfosuccinic acid.

In 1 of the drawings, l designates the separator of the present invention, and 2 denotes lthe integral embossedl ribs thereon.v The w diagrairof IFig. 2 self-explanatory.

EXAMPLE water) 106 Water 281 Tergitol 08 (Sodium salt of sulfated 2-ethyl hexanol, 45% total solids) 25 This resin solution contained about 43 percent by weight of resin solids. Upon saturation of the sheet followed by squeezing, the pick-up of the resin solution was such that the amount of resin left in the sheet was 39% based on the dry sheet plus the resin. The impregnated sheet was then dried, embossed to form spaced parallel ribs Y therein, and cured by passing through a slot formed between two metallic platens heated to about 450-500 F. The emerging cured sheet was then sprayed with a water solution of Tergitol l08 which contained 3% by weight thereof. Some of the water evaporated due to the fact that the cured sheet was at about 400 F. The sheet was then trimmed to width and cut to length to form battery separators which were placed in their shipping containers and allowed to stand for 5-10 hours to effect thorough distribution of the solution of the wetting agent. The wetting agent imparted by the spraying equalled 11/2% of the resin. The resulting battery separators were eminently suitable as replacement for the wood battery separators heretofore employed. The separators of this example were almost instantaneously penetrated by the battery acid when it was added to the battery.

The separators of the present invention do not need to be conditioned or maintained wet until the battery acid is added. Batteries can be assembled dry with the separators of this invention and kept dry indefinitely before the battery acid is added, without any damage.

From the foregoing description, many advantages of our invention will be apparent to those skilled in the art. The principal advantage is that the wetting agent is so introduced that maximum wetting properties are obtained with a minimum amount of wetting agent. Another advantage is that by means of our invention the necessity of using the large amounts of wetting agent which might impair the properties of the separator is obviated. Another advantage is that the wetting agent which is added with the resin solution facilitates greatly the subsequent .penetration of the cured sheet by the later portion of the wetting agent so that with a given total amount of wetting agent our invention gives bet ter and more effective utilization of the wetting agent. As explained above, our addition of the wetting agent both with the resin solution and subsequently to the cured sheet brings about a new cooperation which results in advantages which cannot be obtained'f all of.. the wetting agent is addedin the aqueous solution of the resin or is applied to the cured sheet. Another adzvantage is that our invention is simple to install and lends itself admirably to commercial utiliza; tion. Numerous other advantages of our invene tion will be obviousto those skilled in the art.

The product of the process described hei'eirli is claimed in our copending application Serial No'. 240,3 13l filed of even date herewith.

- Having thusdescribed our invention,` whatwe claim and desire tonprotet by Letters Patent ist' l. The process of malifi'ng aliquid permeable battery separator "which comprises impregnating a bibulous cellulosic fibrous sheet having an alpha cellulose content of at least percent and having an air permeability (Gurley) of from 1 to l-0 seconds with an aqueous solution of an A- stage phenol-formaldehyde resin and a wetting agent, in such manner that said sheet picks up from 25 to 50 percent by weight of said resin based on 'ber plus resin, drying said sheet and thereby depositing said resin and wetting agent in and around the iibers of the sheet in such a way that upon advancing said resin to the C-stage said fibers will be protected against battery acid but the air permeability of the sheet will not be materially lowered, heating the dried sheet to a temperature of from 300 to 550 F. to advance said resin to the C-stage, applying an aqueous solution of the same wetting agent to the cured sheet, and cutting the resulting sheet into battery separators, the wetting agent applied from the aqueous solution of the resin greatly facilitating distribution of the aqueous solution of the wetting agent subsequently applied to the cured sheet, the total amount of said wetting agent introduced into the separator being equal to from 1 to 10 percent by weight based on the cured resin content of the separator, from one-third to onehalf of said wetting agent being applied from said resin solution and the balance of said wetting agent being incorporated with the cured sheet while in aqueous solution, said wetting agent being of a type which facilitates penetration of the v finished separator by the battery acid, being devoid of objectionable contaminating influence in the battery, and being stable to battery acid, introduction of said wetting agent in the two-stage manner described giving results considerably superior to those which would be obtained were the same total amount of wetting agent introduced in only one of said stages.

2. A process as set forth in claim 1 wherein said aqueous solution of said wetting agent is applied by coating the cured sheet While said sheet is at a temperature of from 300 to 500 F. by reason of residual heat from the curing step, with an aqueous solution of the wetting agent, and wherein the thus-coated sheet is allowed subsequently to stand for several hours under relatively nonevaporative conditions, while maintaining said last-named wetting agent dissolved in water, to allow uniform distribution of the wetting agent throughout the separator.

3. A process as set forth in claim l wherein the wetting agent is an alkali metal salt of a sulfated rfatty alcohol having at least eight carbon atoms per molecule.

4. A process as set forth in claim 1 wherein the amount of wetting agent deposited from the aqueous solution of the A-stage resin ranges from 1A? to 1% percent by weight of the resin in the sheet and wherein the amount of wetting agent applied in aqueous solutionto the cured sheet ranges from 1 to 2 percent by Weight of the resin in the sheet.

v5. A process set forth in claim 1 wherein the wetting agent is a sodium salt of sulfated 2-ethyl hexanol and wherein the amount thereof deposited from the aqueous solution of the A-stage resin ranges from 1/2 to 11/2 percent by weight of the resin in the sheet and wherein the amount thereof applied in aqueous solution to the cured sheet ranges from 1 to 2 percent by weight of the resin in the sheet.

EDWIN C. UHLIG.

LINWOOD A. MURRAY, JR.

References Cited in the le 0i' this patent UNITED STATES PATENTS Number Name Date 5 1,802,127 Teague Apr. 2l, 1931 2,103,640 Richter Dec. 28, 1937 2,329,651 Powers et al. Sept. 14, 1943 2,421,363 Young May 27, 1947 2,529,389 Hampton Nov. 7, 1950 l() 2,543,137 Uber Feb. 27, 1951 OTHER REFERENCES McCutcheon, Soap & `Sanitary Chemicals October 1949 page 49. 

1. THE PROCESS OF MAKING A LIQUID PERMEABLE BATTERY SEPARATOR WHICH COMPRISES IMPREGNATING A BIBULOUS CELLULOSIC FIBROUS SHEET HAVING AN ALPHA CELLULOSE CONTENT OF AT LEAST 90 PERCENT AND HAVING AN AIR PERMEABILITY (GURLEY) OF FROM 1 TO 10 SECONDS WITH AN AQUEOUS SOLUTION OF AN ASTAGE PHENOL-FORMALDEHYDE RESIN AND A WETTING AGENT, IN SUCH MANNER THAT SAID SHEET PICKS UP FROM 25 TO 50 PERCENT BY WEIGHT OF SAID RESIN BASED ON FIBER PLUS RESIN, DRYING SAID SHEET AND THEREBY DEPOSITING SAID RESIN AND WETTING AGENT IN AND AROUND THE FIBERS OF THE SHEET AND THERETHAT UPON ADVANCING SAID RESIN TO THE C-STAGE SAID FIBERS WILL BE PROTECTED AGAINST BATTERY ACID BUT THE AIR PERMEABILITY OF THE SHEET WILL NOT BE MATERIALLY LOWERED, HEATING THE DRIED SHEET TO A TEMPERATURE OF FROM 300* TO 550* F. TO ADVANCE SAID RESIN TO THE C-STAGE, APPLYING AN AQUEOUS SOLUTION OF THE SAME WETTING AGENT TO THE CURED SHEET, AND CUTTING THE RESULTING SHEET INTO BATTERY SEPARATORS, THE WETTING AGENT APPLIED FROM THE AQUEOUS SOLUTION OF THE RESIN GREATLY FACILITATING DISTRIBUTION OF THE AQUEOUS SOLUTION OF THE WETTING AGENT SUBSEQUENTLY APPLIED TO THE CURED SHEET, THE TOTAL AMOUNT OF SAID WETTING AGENT INTRODUCED INTO THE SEPARATOR BEING EQUAL TO FROM 1 TO 10 PERCENT BY WEIGHT BASED ON THE CURED RESIN CONTENT OF THE SEPARATOR, FROM ONE-THIRD TO ONEHALF OF SAID WETTING AGENT BEING APPLIED FROM 